When using a cellular network, in general, a user either has complete access to the network or no access to the network. Thus, unless a user's equipment (UE) lacks certain capabilities (e.g., it is too old to provide video playback), the UE is able to access all voice and data services (e.g., internet access, video calling, text messaging, etc.) over the network.
Similarly, when roaming, users generally also have complete access or no access. So, a user associated with first provider, but roaming on a second provider's network, has access to all voice and data services. Roaming contracts between providers tend not to contract out specific services because no practical mechanism existed to provide different levels of service (e.g., voice only, voice and text only, data only, etc.).